This invention relates to a humidity regulating apparatus whereby the humidity inside a semi-sealed container having an interior indirectly exposed to outside air can be regulated, and particularly to such an apparatus for a magnetic disk drive.
FIG. 1 is a partial cross-sectional diagram illustrating a conventional magnetic disk drive having a humidity regulating apparatus. Such a diagram is described on page 17 of paper No. 46-2 "TRIBOLOGY FOR MAGNETIC DISK STORAGE" of the No. 36 research association materials of a meeting of The Magnetics Society of Japan (Corporation) (held at the Kikai Shinko Hall July 21, 1986) titled MAGNETIC RECORDING (MAGNETIC RECORDING AND TRIBOLOGY). FIG. 2 is a graph of the adsorptive quantity of moisture of silica gel based on a wt% ratio of absorbed water per absorbent (g:g) listed, for example, on page 854 of the Handbook of Chemical Engineering (editor: Chemical Engineering Society of Japan) issued by Maruzen Co., Ltd. (2-6 Nihonbashi-doori, Chuo-ku Tokyo).
In FIG. 1 semi-sealed type container 1 for magnetic disk drive comprises a base 2 and a case 3 that is secured in a sealed manner on the base 2. Several ventilation holes 4 are provided in the top of case 3. Cap 5 is secured on the top of case 3 to cover the ventilation holes 4. Several ventilation holes 6 are provided in cap 5. Primary filter 7 is fitted inside cap 5 between ventilation holes 4 and 6. Filter case 8 is secured to the inner surface of case 3. Secondary filter 9 is fitted inside filter case 8 and covers ventilation holes 4. Throttle 12 is fitted into the top of absorbent case 11. Filter 14 is inserted between throttle 12 and silica gel 13.
A container of a conventional humidity regulating apparatus used in magnetic disk drives encloses a disk that is driven and rotated, a head that is held in proximity to the recording surface of the disk thereof and an actuator that causes the head to move in the radial direction of the disk.
Outside air is sucked in by rotation of the disk is cleaned by passing through ventilation holes 6 of cap 5,. primary filter 7, ventilation holes 4 of case 3, secondary filter 9 and throttle 10 of filter case 8,. and flows into the inside of container 1. Water in the outside air also enters the container 1 through diffusion and the humidity inside the container rises. If rotation of the disk is stopped and the head is made to contact the disk in this state,. there is a danger of stiction wherein the head sticks to the disk. The disk, and possibly the head can be damaged if the disk drive is restarted in this condition.
A moisture adsorption device, including silica gel 13 in the absorbent case 11, is provided inside container 1 to adsorb the water that has entered. Further, throttle 12 provided at absorbent case 11 controls the adsorptive quantity of the water and prevents the inside of container 1 from attaining excessively low humidity.
Silica gel 13 is porous, and its surface area per unit weight is extremely large. Further, the absorptive quantity of moisture of silica gel 13 is almost proportional to humidity within a range of humidity in which the gel structure is maintained as illustrated in FIG. 2. However, when the humidity rises and the water content increases, a state of saturation is reached. In a conventional humidity regulating apparatus such as described aboVe. When the adsorptive quantity of moisture in silica gel 13 reaches a state of saturation, the capability to adsorb water is lost even if the humidity rises excessively.
Furthermore, there have been problems in that the adsorptive quantity of moisture could not be regulated if the size of throttle 10 that regulates the suction of the outside air and the size of throttle 12 that controls the adsorptive quantity of moisture were fixed and in that the humidity inside container 1 could not be regulated in accordance with changes in the humidity of the outside air.